5NT "Pick a slam"

It has now become the norm at the expert level to use 5NT where a trump suit has not been firmly agreed as “pick a slam.” The advent of Roman Key Card Blackwood means that 5NT as a Grand Slam Force is really necessary only when the inquirer has a void. Using 5NT to instruct partner to pick a slam occurs most often when at least three strains are in play.

Suppose that responder to 1NT has

                    ♠ 4

                    ♥ A J 6 3

                    ♦ K Q J 2

                    ♣ K Q J 4

                 West         East

                       1NT          2♣

                        2♠            5NT

In general, 5NT is not needed as a Grand Slam Force because such hands can be handled with a 4NT Roman Key Card bid. 

5NT bid is often useful in a competitive auction.

                    ♠ —

                    ♥ K 3

                    ♦ K Q 6 4 2

                    ♣ A Q 8 7 5 3

                West     North     East     South

                2♠         3♥         4♠       5NT

North is invited to bid 6♣, 6♦ or 6♥. This use of the 5NT bid has diminished the use of the Grand Slam Force. 

SOURCE: "Bidding", The Official ACBL Encyclopedia of Bridge, 7th ed. Horn Lake: American Contract Bridge League, Inc., 2011, page 227. Print